JP2006313584A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a magnetic recording medium having excellent floating properties and reliability with high yield by suppressing a protrusion on a medium surface by deposition of a big silicon oxide generated when a granular recording layer containing Si and oxygen is film-deposited. <P>SOLUTION: The recording layer is film-deposited by a sputtering method using a target formed by mixing an alloy containing at least Co and a crystalline SiO<SB>2</SB>powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium applied to perpendicular magnetic recording technology.

  In order to increase the capacity of a magnetic recording apparatus, a perpendicular magnetic recording method has attracted attention as a technique for increasing the surface recording density. The perpendicular magnetic recording method is a method in which the recording bits are formed so that the magnetization of the recording medium is perpendicular to the medium surface and the magnetizations in adjacent recording bits are antiparallel to each other. In the perpendicular magnetic recording method, since the demagnetizing field in the magnetization transition region is small, a steep magnetization transition region is formed as compared with the in-plane magnetic recording method, and the magnetization is stabilized at a high density. Therefore, compared with the in-plane magnetic recording system, the film thickness can be increased to increase the magnetic particle volume in order to obtain the same recording resolution, and the decay of recorded magnetization over time, that is, thermal demagnetization can be reduced. Can be suppressed. Furthermore, a combination of a single magnetic pole head and a perpendicular magnetic recording medium having a perpendicular recording layer and a soft magnetic underlayer provides a high recording magnetic field, and a material having high magnetic anisotropy can be selected for the perpendicular recording layer. Thus, thermal demagnetization can be further suppressed.

Currently, a CoCr-based alloy crystalline film is mainly used as a recording layer material for perpendicular magnetic recording media. By controlling the crystal orientation so that the c-axis of the CoCr crystal having the hcp structure is perpendicular to the medium surface, the easy magnetization axis of the recording layer can be kept perpendicular to the medium surface. Here, by reducing the size of the CoCr-based alloy crystal grains and reducing the variation, and reducing the magnetic interaction between the grains, the medium noise can be reduced and the recording density can be improved. As one method for controlling such a recording layer structure, a recording layer generally called a granular film has been proposed in which ferromagnetic particles are surrounded by a nonmagnetic substance such as an oxide. In the granular recording layer, the nonmagnetic grain boundary phase separates the magnetic particles, reduces the interaction between the magnetic particles, and reduces noise in the magnetization transition region. Japanese Patent Application Laid-Open No. 2003-178413 discloses a perpendicular magnetic recording medium having a recording layer made of a ferromagnetic alloy containing Co and Pt and an oxide having a volume density of 15% to 40%. IEEE Transactions on Magnetics, Vol. 40, No. 4, July 2004, pp. 2498-2500, “Role of Oxygen Incorporation in Co-Cr-Pt-Si-O Perpendicular Magentic Recording Media” includes CoCrPt alloy and A method of forming a recording layer having a granular structure by DC magnetron sputtering in an argon-oxygen mixed gas atmosphere using a composite target containing SiO ₂ is disclosed. It has been reported that reactive sputtering in an oxygen-containing atmosphere increases the coercive force and improves the recording / reproducing characteristics.

  In addition, a magnetic recording medium having a recording layer having a granular structure is also disclosed in Japanese Patent Application Laid-Open No. 2003-178423 as a magnetic recording medium used in a conventionally used in-plane magnetic recording system.

JP 2003-178413 A JP 2003-178423 A IEEE Transactions on Magnetics, Vol.40, No.4, July 2004, pp. 2498-2500

In the method for manufacturing the magnetic recording medium, as a target for forming the recording layer, a target formed by mixing a CoCrPt alloy and powdered amorphous SiO ₂ by a sintering method or the like is generally used. Is. In this manufacturing method, there is a problem in that a relatively large size silicon oxide is scattered from the target during the sputtering process, and is deposited on the medium, resulting in a protrusion defect. When the flying height of the magnetic head is lower than 20 nm, the magnetic head and the magnetic recording medium may be damaged due to the collision between the magnetic head and the protrusion, and the apparatus may be broken. In addition, even when protrusions are removed during the surface polishing process of the magnetic recording medium, the flying property and corrosion resistance are significantly deteriorated due to the lack of the recording layer and the protective layer at the removed part and damage to the surface of the medium due to the peeled particles. There is a problem to make.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method of manufacturing a magnetic recording medium that is excellent in floating property and corrosion resistance and reduces the failure occurrence rate of a magnetic recording device.

In order to achieve the above object, the present invention provides a recording layer comprising a nonmagnetic crystal grain boundary composed mainly of a crystal grain having magnetism and a Si oxide surrounding it on a nonmagnetic substrate by a sputtering method. When forming, a recording layer is formed by a sputtering method using a target in which an alloy containing at least Co and crystalline SiO ₂ powder are mixed. As the sputtering method, DC sputtering, a sputtering method using a DC pulse power source (DC pulse sputtering method), or an RF sputtering method can be used.

According to the present invention, a recording layer is formed by sputtering using a target mixed with crystalline SiO ₂ powder, thereby preventing enormous silicon oxide particles from flying from the target and reducing projections on the surface of the medium. To do. As a result, it is possible to provide a method for manufacturing a magnetic recording medium that is excellent in flying property and reliability and has a high yield.

  Embodiments in which the manufacturing method of the present invention is applied to a perpendicular magnetic recording medium and a longitudinal magnetic recording medium will be described below with reference to the drawings.

The perpendicular magnetic recording medium of this example was formed using an in-line type sputtering apparatus shown in FIG. Each chamber is independently evacuated. All the process chambers were evacuated in advance to a vacuum of 1 × 10 ⁻⁵ Pa or less, and the process was sequentially performed by moving the carrier supporting the substrate to each process chamber. The carbon protective layer was formed by chemical vapor deposition (CVD), and the other layers were formed by DC magnetron sputtering.

  FIG. 3 is a schematic diagram of a cross-sectional structure of a perpendicular magnetic recording medium manufactured by the manufacturing method of Example 1. This perpendicular magnetic recording medium has a structure in which a seed layer 12, a soft magnetic underlayer 13, a particle size control layer 14, a granular recording layer 15, a protective layer 16, and a liquid lubricating layer 17 are sequentially laminated on a substrate 11. However, the structure shown in FIG. 3 shows an example, and the perpendicular magnetic recording medium manufactured by the manufacturing method of the present invention is not limited to the structure shown in FIG.

  FIG. 4 is a schematic view of the production procedure of this medium, and the production conditions are shown below. As the substrate 11, a glass substrate having a diameter of 63.5 mm was used. The substrate 11 is carried from the substrate carry-in chamber 201, and after evacuation, the substrate is transferred to the seed layer forming chamber 202, and a 30 nm thick seed layer made of a NiTa alloy is formed on the substrate 11 in order to improve adhesion to the substrate. 12 was formed. Here, the film formation of the seed layer 12 is performed using Ni-37.5 at. A% Ta target was used. The seed layer 12 only needs to ensure adhesion to both the substrate and the layer above the seed layer, and any of Ni-based alloys, Co-based alloys, Al-based alloys, and the like can be used. For example, a NiTaZr alloy, NiAl alloy, CoTi alloy, AlTa alloy, or the like can be used.

  Next, in the soft magnetic layer forming chambers 203 to 205, the CoTaZr alloy was formed to 50 nm, Ru was 0.8 nm, and the CoTaZr alloy was sequentially formed to 50 nm, so that the soft magnetic layer 13 was composed of three layers. Here, for the formation of the CoTaZr layer, Co-3at. % Ta-5 at. A% Zr target was used. With such a three-layer structure, the upper and lower CoTaZr alloy layers are antiferromagnetically coupled via the Ru layer, and noise caused by the soft magnetic layer can be reduced.

  The soft magnetic material and the film thickness may be selected within a range in which sufficient overwrite characteristics can be obtained at the time of recording. For example, instead of a CoTaZr alloy, a material such as a CoNbZr alloy, a CoTaNb alloy, or an FeCoB alloy may be used. There is no problem if the film thickness of the entire soft magnetic layer material is 50 nm to 300 nm. The structure of the soft magnetic layer includes a structure in which a magnetic domain control layer for fixing the magnetic domain of the soft magnetic layer is provided under a soft magnetic layer made of a soft magnetic material such as a CoTaZr alloy, or the three layers as described above. A structure in which a magnetic domain control layer is provided under the structure may be used.

Next, in the intermediate layer forming chambers 206 and 207, Ta having a thickness of 1 nm and Ru having a thickness of 20 nm were sequentially formed. The intermediate layer 14 controls the crystal orientation and crystal grain size of the recording layer, and plays an important role in reducing exchange coupling between crystal grains of the recording layer. The film thickness, configuration, and material of the intermediate layer 14 may be set within a range in which the above effects can be obtained, and are not particularly limited to the above film thickness, configuration, and material. In the intermediate layer configuration, the role of the Ta layer is to enhance the c-axis orientation in the direction perpendicular to the Ru film surface. The film thickness may be set within a range where this is satisfied, and a value of about 1 nm to 5 nm is usually used. Instead of Ta, a Pd, Pt, Cu having a face-centered cubic lattice (fcc) structure, an alloy containing these, a ferromagnetic FCC material such as NiFe, or a material having an amorphous structure such as NiTa may be used. May be. The role of the Ru layer is to control the crystal grain size and crystal orientation of the recording layer and to reduce exchange coupling between crystal grains. The film thickness may be set within a range where this is satisfied, and a value of about 3 nm to 30 nm is usually used. Further, instead of Ru, an alloy containing Ru as a main component or Ru containing an oxide such as SiO ₂ may be used.

Next, after transporting to the recording layer forming chamber 208, an argon-oxygen mixed gas was introduced to form a recording layer 15 having a film thickness of 14 nm, and then evacuating to 0.5 Pa or less to reduce oxygen remaining in the chamber. For formation of the recording layer 15, Co-13 at. % Cr-20 at. An alloy-oxide composite type target prepared by mixing a% Pt alloy and crystalline SiO ₂ having a particle diameter of 1 μm at a ratio of 88:12 mol% and using a sintering method was used. The film formation rate when forming the recording layer 15 was 2.6 nm / s.

  Subsequently, after transporting to the carbon protective layer forming chamber 209, a DLC (diamond-like carbon) film having a thickness of 4 nm was formed as the protective layer 16 by a chemical vapor deposition method (CVD method). Subsequently, the substrate was unloaded to the substrate unloading chamber 210, then opened to the atmosphere and taken out from the sputtering apparatus, and an organic lubricant was applied to the surface to form the lubricating layer 17.

  Argon gas was used as the sputtering gas when forming the Ru layer of the intermediate layer 14. If the gas pressure is about 2 Pa to 6 Pa, there is no problem, but here it was 5 Pa. When the recording layer 15 is formed, there is no problem if a mixed gas of argon and oxygen is used as the sputtering gas and the total gas pressure is about 3 Pa to 6 Pa, but here it is 4 Pa. What is necessary is just to set the oxygen concentration in argon oxygen mixed gas in the range in which sufficient SNR is obtained, and it was 2.5% here. When the carbon protective layer was formed, a gas in which 20% and 2% of hydrogen and nitrogen were mixed with ethylene was used, and the total gas pressure was 2 Pa. When forming the other layers, 1 Pa was used, and argon gas was used as the sputtering gas.

For comparison between Example 1 and the conventional manufacturing method, a manufacturing method including a step of forming the recording layer 15 by sputtering using a target containing amorphous SiO ₂ was set as Comparative Example 1. In the production method of Comparative Example 1, Co-13 at. % Cr-20 at. % Pt alloy and amorphous SiO ₂ having a particle diameter of 1 μm were mixed at a ratio of 88:12 mol%, and the recording layer 15 was formed using a target formed by a sintering method. The film configuration and manufacturing conditions other than the recording layer target were the same as those in Example 1.

The crystal structure of the SiO ₂ powder added to the target was evaluated using an X-ray diffractometer using CuKα rays. For the evaluation of the number of surface protrusions of the magnetic recording medium, the number of protrusions of 0.2 μm or more per medium surface was measured using an optical surface inspection apparatus. The signal-medium noise ratio SNRd of the manufactured magnetic recording medium was evaluated using a general recording / reproducing characteristic evaluation tester using a composite single pole head having a recording head width of 170 nm and a reproducing head width of 125 nm. The SNRd was evaluated by the ratio of reproduction output and medium noise at a linear recording density of 15.7 kfr / mm.

FIG. 5 shows an X-ray diffraction diagram of the crystalline SiO ₂ powder added to the target of the recording layer used in Example 1. FIG. 6 shows an X-ray diffraction diagram of the amorphous SiO ₂ powder added to the target of the recording layer used in Comparative Example 1. As shown in FIG. 5, the SiO ₂ powder added to the target of the recording layer used in the production method of the present invention has a maximum intensity peak at a Bragg angle 2θ = 26.6 ± 0.1 °.

  FIG. 7 shows an X-ray diffraction diagram of the target of the recording layer used in the manufacturing method of Example 1. FIG. 8 shows an X-ray diffraction diagram of the target of the recording layer used in the manufacturing method of Comparative Example 1. As shown in FIG. 7, the target of the recording layer used in the manufacturing method of the present invention also has a peak at the Bragg angle 2θ = 26.6 ± 0.1 °.

  FIG. 1 shows the transition of the number of protrusions of 0.2 μm or more on the surface of the medium when 3000 perpendicular magnetic recording media were produced by the manufacturing method of Example 1 and Comparative Example 1, depending on the number of deposited films. Immediately after the start of film formation, the number of protrusions is large in any of the manufacturing methods due to the influence of impurities on the surface of the target. In the subsequent film formation, the number of protrusions was always in a good state of 200 or less per surface. On the other hand, in Comparative Example 1, the number of protrusions that were 200 or less was about 500, which was larger than that in Example 1, and there was a medium in which the number of protrusions was 200 or more in the subsequent film formation.

9 and 10 show surface micrographs of the target of the recording layer used in Example 1 and Comparative Example 1 after 3000 film formation, respectively. In the target used in Comparative Example 1, the surface was rough, whereas the surface unevenness period of the target used in Example 1 was small and comparatively smooth. This is presumably because large SiO ₂ particles were generated by sputtering in the target used in Comparative Example 1.

The above results are discussed below. In crystalline SiO ₂ powder, Si atoms and O atoms form a SiO ₄ tetrahedral structure by covalent bonds, and all O atoms of the tetrahedron are shared and connected to another tetrahedron. Bonding power is very strong. On the other hand, the amorphous SiO ₂ powder has a SiO ₄ tetrahedral structure, but each tetrahedron is bonded randomly, and its bonding strength is weaker than crystalline SiO ₂ . Accordingly, when a target containing amorphous SiO ₂ is used, relatively small size silicon oxide particles are detached from the powder from weakly bonded portions at low collision energy, and this reaches the surface of the medium and causes protrusion defects. It seems to be a cause. On the other hand, when a target containing crystalline SiO ₂ is used, it is considered that the energy at which particles are separated from the SiO ₂ powder is high and uniform, the probability that large-sized particles are separated decreases, and the number of protrusion defects decreases.

  Table 1 shows the yield rate evaluated by the medium signal / noise ratio SNRd of the perpendicular magnetic recording medium manufactured by the manufacturing method of Example 1 and Comparative Example 1 and the output fluctuation caused by the medium defect. SNRd showed the same value in Example 1 and Comparative Example 1, and the electromagnetic conversion characteristics of the magnetic recording medium produced by the production method of Example 1 were at a level comparable to Comparative Example 1. On the other hand, protrusion defects were reduced in the magnetic recording medium produced by the production method of Example 1, and the yield rate was improved.

In addition, in the SiO ₂ powder to be added to the target, when crystalline SiO ₂ powder and amorphous SiO ₂ powder are mixed, large particles fly from the amorphous SiO ₂ powder to cause protrusion defects, so that sufficient yield is achieved. The improvement effect cannot be obtained. Therefore, in the method for manufacturing a magnetic recording medium of the present invention, it is obvious that the maximum effect can be obtained by changing the total amount of SiO ₂ powder added to the target for forming the granular recording layer to crystalline SiO ₂ powder.

  FIG. 11 is a schematic diagram of a cross-sectional structure of a longitudinal magnetic recording medium manufactured by the manufacturing method of Example 2. This longitudinal magnetic recording medium includes a first seed layer 102, a second seed layer 103, an underlayer 104, a first recording layer 105, a Ru intermediate layer 106, a second recording layer 107, a protective layer 108, a liquid on a substrate 101. The lubrication layer 109 is sequentially laminated. However, the structure shown in FIG. 11 shows an example, and the longitudinal magnetic recording medium manufactured by the manufacturing method of the present invention is not limited to the structure shown in FIG.

  The conditions for producing the medium are shown below. As the substrate 101, a glass substrate having a diameter of 63.5 mm was used. A 30 nm-thick first seed layer 102 made of a Ti—Al alloy was formed on the substrate 101 by a sputtering method. Here, for forming the first seed layer 102, Ti-52at. A% Al target was used. Next, a 30-nm second seed layer 103 made of a Ru—Al alloy was formed by sputtering. Here, for the formation of the second seed layer 103, Ru-50at. A% Al target was used. Further thereon, an underlayer 104 made of a Cr—Mo alloy with a thickness of 5 nm was formed by sputtering. Here, Cr-20 at. A% Mo target was used.

  A 5 nm first recording layer 105, a 0.6 nm Ru intermediate layer 106, and a 15 nm second recording layer 107 were sequentially formed on the base layer 104. The recording layer has such a three-layer structure, and the first recording layer 105 and the second recording layer 107 are antiferromagnetically coupled via the Ru intermediate layer 106, thereby being excellent in thermal fluctuation resistance and medium noise. It is generally known that can be reduced.

Here, the first recording layer 105 and the second recording layer 107 are mixed with argon and oxygen using a target in which a CoCrPt alloy and crystalline SiO ₂ powder are mixed, as in the manufacturing method of the first embodiment. It was formed by DC sputtering in an atmosphere. For the formation of the first recording layer 105, Co-12 at. % Cr-12 at. A target in which a% Pt alloy and crystalline SiO ₂ having a particle diameter of 1 μm were mixed at a ratio of 94: 6 mol% was used. For the formation of the second recording layer 107, Co-11at. % Cr-13 at. A target in which a% Pt alloy and crystalline SiO ₂ having a particle diameter of 1 μm were mixed at a ratio of 93: 7 mol% was used.

  Subsequently, similarly to the manufacturing method of the first example, a DLC protective film 108 having a thickness of 4 nm was formed by a CVD method, and after carrying out from the film forming apparatus, a lubricating layer 109 was formed.

To evaluate the effect of the manufacturing method of the present invention, the SiO ₂ to be added to the target as an amorphous SiO ₂ in place of the crystalline SiO _2, to form the first recording layer 105 and the second recording layer 107 The manufacturing method including the process was referred to as Comparative Example 2.

Table 2 shows the yield rate evaluated by the output fluctuation caused by the medium defect. In the longitudinal recording medium, since the film thickness is generally smaller than that of the perpendicular recording medium and the scratch resistance is good, the yield rate is good, but the manufacturing method of Example 2 using a target to which crystalline SiO ₂ is added is used. It became clear that the yield was improved as compared with the production method of Comparative Example 2.

  As described above, the magnetic recording medium manufacturing method of the present invention makes it possible to provide a magnetic recording medium that has excellent flying characteristics and corrosion resistance and reduces the failure rate of the magnetic recording apparatus. In particular, the productivity could be remarkably improved in a perpendicular magnetic recording medium having a larger film thickness than the longitudinal recording medium.

6 is a graph showing the transition of the number of surface protrusion defects of a perpendicular magnetic recording medium according to the number of deposited films by the manufacturing methods of Example 1 and Comparative Example 1. 2 is a diagram schematically showing a perpendicular magnetic recording medium film forming apparatus in the manufacturing method of Example 1. FIG. 3 is a diagram schematically showing a cross-sectional configuration of a perpendicular magnetic recording medium manufactured by the manufacturing method of Example 1. FIG. 6 is a diagram showing a film forming process of a perpendicular magnetic recording medium in the manufacturing method of Example 1. FIG. 3 is a graph showing an X-ray diffraction diagram of crystalline SiO ₂ powder added to the target of the recording layer used in the manufacturing method of Example 1. FIG. 3 is a graph showing an X-ray diffraction diagram of amorphous SiO ₂ powder added to a target of a recording layer used in the manufacturing method of Comparative Example 1. FIG. 2 is a graph showing an X-ray diffraction diagram of a recording layer target used in the manufacturing method of Example 1. FIG. 6 is a graph showing an X-ray diffraction diagram of a recording layer target used in the manufacturing method of Comparative Example 1. FIG. It is the surface microscope photograph after 3000 film-forming of the target of the recording layer used with the manufacturing method of Example 1. It is the surface micrograph after 3000 film-forming of the target of the recording layer used with the manufacturing method of the comparative example 1. 6 is a diagram schematically showing a cross-sectional configuration of a longitudinal magnetic recording medium manufactured by the manufacturing method of Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Perpendicular magnetic recording medium, 11 ... Nonmagnetic substrate, 12 ... Seed layer, 13 ... Soft-magnetic underlayer, 14 ... Grain size control layer, 15 ... Granular recording layer, 16 ... Protective layer, 17 ... Liquid lubricating layer, 101 ... Nonmagnetic substrate, 102 ... First seed layer, 103 ... Second seed layer, 104 ... Underlayer, 105 ... First recording layer, 106 ... Ru intermediate layer, 107 ... Second recording layer, 108 ... Protective layer, 109 DESCRIPTION OF SYMBOLS ... Liquid lubrication layer, 201 ... Substrate introduction chamber, 202 ... Seed layer formation chamber, 203-205 ... Soft magnetic layer formation chamber, 206, 207 ... Intermediate layer formation chamber, 208 ... Recording layer formation chamber, 209 ... Protection layer formation chamber 210 ... Substrate unloading chamber

Claims (4)

A magnetic recording medium comprising: a step of forming a nonmagnetic underlayer on a nonmagnetic substrate; and a step of forming a recording layer containing at least Co, silicon, and oxygen on the nonmagnetic underlayer by a sputtering method. In the manufacturing method of
A method for producing a magnetic recording medium, wherein a sputtering target used in the step of forming the recording layer includes at least Co or an alloy containing Co and silicon dioxide powder, and the silicon dioxide powder is crystalline.   The silicon dioxide powder contained in the sputtering target has a maximum diffraction peak at a Bragg angle (2θ) of 26.6 ± 0.1 ° in a powder X-ray diffraction spectrum by CuKα rays. A method for producing the magnetic recording medium according to 1.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the sputtering target has a diffraction peak at a Bragg angle (2θ) of 26.6 ± 0.1 ° in an X-ray diffraction spectrum by CuKα rays. .   The method of manufacturing a magnetic recording medium according to claim 1, comprising a step of forming a soft magnetic underlayer on the nonmagnetic substrate and a step of forming an intermediate layer.

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